1. Field of the Invention
The present invention relates to a navigation system for searching a route between a start position and a destination to guide a vehicle to the destination, and more particularly to an improvement in input operation for the destination.
2. Description of the Prior Art
FIG. 1 shows a construction of a conventional navigation system as described in Japanese Patent Laid-open Publication No. 2-166600, for example. Referring to FIG. 1, reference numeral 1 designates input means for inputting a start position, a destination, etc. Reference numeral 2 designates signal processing means composed of computing means 22 and display control means 23. The computing means 22 detects a vehicle position on the basis of an azimuth detection signal and a distance detection signal from vehicle position detecting means 6, and selects a data from a road network database 5a to calculate a shortest distance. The display control means 23 performs control of display.
Reference numeral 5 designates map data storing means, such as a CD-ROM, composed of the road network database 5a and a road map database 5b. The road network database 5a preliminarily stores a plurality of road network data each composed of roads between a start position and a destination area connected together through a trunk road. The road map database 5b preliminarily stores road map data containing coordinate information, which is used in a general navigation system. The vehicle position detecting means 6 detects an azimuth and a distance. Reference numeral 7 designates display means such as a CRT. The display means 7 is controlled by the display control means 23.
In operation, when a start position and a destination are input from the input means 1 such as a ten-key pad, the computing means 22 computes a vehicle position on the basis of an azimuth detection signal and a distance detection signal from the vehicle position detecting means 6, and selects data from the road network database 5a to calculate a shortest distance from the vehicle position to the destination.
The display control means 23 decides a shortest route from the vehicle position to the destination on the basis of data from the road map database 5b, and the display means 7 displays the shortest route decided above. As mentioned above, in the conventional navigation system, when the start position as a single point and the destination as a single point are input, the shortest route to the destination is automatically searched and displayed.
However, even when an operator does not intend to specify the destination as a single point, the single point on the map has to be specified in the system. In most cases, during travelling of the vehicle, it is required to guide a route to a trunk road or indicate any one of plural destinations existing in the periphery of the vehicle present position. In such cases, the operator must search the map, so that the input operation becomes complicated.